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Dynamics of the herbaceous layer in a dry deciduous forest of south India (Bandipur National Park)

Dynamics of the herbaceous layer in a dry deciduous forest of south India (Bandipur National Park)
Shridhar Devidas

1995

Salim Ali School of Ecology and Environmental Sciences, Pondicherry University, Pondicherry 605 014, INDIA.

ABSTRACT

The grass layer seems well adapted to disturbance in the form of grazing and fire. The primary production values of the herbaceous layer indicate that this ecosystem is not impoverished by the producers, since the amount of nitrogen produced in the soil and its uptake is synchronised. But the loss of phytomass through consumption by the herbivores (64 % of the aboveground production during 1993) seems substantial enough to reduce the grass cover. While analysing the effect of fire on the herbaceous stratum it could be observed that the extent of grass and herb cover is more in the more fire frequented plot. The fire is seen to have detrimental effect on trees and shrubs, by retarding any recruitment of individuals into the bigger girth and height classes.

These findings offer an insight for formulating management plans for the National Park. The dry deciduous forest of Ainurmarigudi Reserve Forest seems to be unpredictable with respect to its dynamics and relationships with environmental factors. Significant relationships were not established between the aboveground phytomass production and climatic parameters. Consequently, predictions of the primary production values of the whole of the National Park is not possible.

Another aspect of importance in this ecosystem where the herbivores are predominantly grazers, is the maintenance of the herb layer to sustain them. But in order to support the mixed feeders (elephants) the presence of the boreal species is indispensable. Total protection from fire leads to a closure of the vegetation retarding grass growth. While in contrast protecting the herb layer from herbivores would lead to an accumulation of dead vegetation. The occurrence of fire under such circumstances often turns uncontrollable destroying the juvenile tree individuals and scalding the mature ones. In order to avoid such catastrophes it seems sensible to cool burn the ground vegetation rotationally in the National Park early in the season.

Much depends on the objectives of the managers of the National Park. If the objective is the conservation of biodiversity, then total protection against fire and herbivores can be argued for. However if the maintenance of the herbivore population is the objective, then the predominance of either the tree/shrubs or the grass alone will have detrimental effect on the herbivore populations. To conclude. “The management of a savanna should include, as part of the objectives, deliberate manipulation of the system to gain knowledge about that system which will aid in the formulation of optimal management policies” (Walker and Noy-Meir. 1982).